Two green inhibitor formulations have been developed for treating aluminum alloys 2024-T3 and 6061-T6. The formulation consists of the oxoanion MnO4− with a catalytic amount of either Cr(VI) (50μg/L present as dichromate) or acetic acid. Both formulations are considered green since they contain Cr(VI) concentrations that are below the EPA safe limit for drinking water that is 100μg/L. The inhibitor formulations have been previously tested on anodized aluminum alloy coupons followed by sealing in a bath containing the inhibitor formulation. The combination of anodizing and sealing lasted over 9 months in a salt fog prohesion test environment1.

Although, this formulation has been shown to work on anodized systems, the largest impact for Cr(VI) replacement will come from conversion (immersion) coating applications. This paper presents the results of how these green inhibitor formulations perform on a non-anodized surface.

Aluminum alloy coupons (2024-T3 , 6061-T6 and 7075-T6) treated with both formulations along with a matrix of their components were tested using anodic potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and ASTM B117 Salt Fog Testing that included unpainted and painted samples with and without scribes. The electrochemical test results are compared against salt spray data, and the correlation between the two approaches is discussed.

Subject
Salt formation, Test methods, Oxide formation, Oxide layers, Acidity, Inhibitor treatment, Corrosion inhibitors, Salt spray corrosion testing, Acetic acid, Pitting, Aluminum alloys, Blistering, Samples
Keywords:
Aluminum, immersion coating, corrosion, green inhibitor, hexavalent chromium
© 2001 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2001
Association for Materials Protection and Performance (AMPP)
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